Our user group studies the human immune response to pathogens and the active immunization of patients against cancer. We interface the biology of human dendritic cells (DCs) with their use as antigen presenting cells to monitor and manipulate the human immune response, including in vivo. Our current FACS analysis instrument is unable to meet our funded needs for 4 reasons. 1) The existing university-run FACS facility has greatly expanded in use. 2) The capacity to assess the human immune response has likewise expanded, particularly because of methods to quantify antigen-specific T cells and to monitor the intracellular accumulation of cytokines in response to antigen-stimulation. 3) It is feasible to use DCs to monitor and manipulate critical aspects of the human immune response in disease states. DCs can now be generated in large numbers and cryopreserved following their uptake and presentation of clinically relevant antigens delivered via recombinant viral vectors and dead tumor cells. These DCs can now be used to monitor the immune response, using FACS-based assays, to chronic viral infections (Epstein Barr Virus and HIV-1) and to tumors (EBV-associated malignancy, melanoma, myeloma). Furthermore DCs can be used to manipulate the human immune response in situ, to actively immunize cancer patients with mature DCs and to silence reactive T cells with immature DCs. 4) Training programs at the pre- and postdoctoral level, including awardees of K08 and K23 grants, are increasingly directed to the study of human DCs and the human immune response. For these reasons we are requesting a FACS Calibur instrument to meet the needs of the user group for multiparameter analyses of human DCs and the human immune response, particularly in the setting of pathogens and active immunization protocols. [unreadable] [unreadable]